1. Field of the Invention
This invention relates to a suspension insulator which is mainly used to form insulator strings to be supported by arms of transmission line towers. More particularly, the invention relates to a suspension insulator whose dimensions are in such a range that its size is reduced without weakening its tensile strength.
2. Related Art Statement
Referring to FIG. 5, a typical conventional suspension insulator uses an insulating member 1 having a shed 1a extending radially from a central core 1c. A metal cap 3 is firmly secured to the top of the core 1c by cement 2. The core 1c has a pin-receiving hole 1d formed therein so as to have a closed top, and sands 5 are deposited on the inner surface of the pin-receiving hole 1d and on the outer sufface of core 1c. A metal pin 4 is inserted to the inside of the core 1c and secured thereto by cement 2a (FIG. 4). In the example of FIG. 4, the metal pin 4 has a large-diameter portion 4a at that end thereof which is buried in the pin-receiving hole 1d of the insulating member 1 by the cement 2a. The metal pin 4 also has a buried rod portion 4b which is cemented to the pin-receiving hole 1d, too.
The inside diameter D of the metal cap 3 has been selected independently of the outside diameter d.sub.2 of the large-diameter portion 4a of the metal pin 4 and the outside diameter d.sub.1 of the buried rod portion of the metal pin 4. In other words, no special attention has been paid to the following ratios M1 and M2 EQU M1=(d.sub.2 -d.sub.1)/d.sub.1, M2=(D-d.sub.2)/d.sub.2
Thus, the above-mentioned diameters D, d.sub.1 and d.sub.2 have been determined without considering the values of the ratios M1 and M2 which are defined above.
The inventors have found that neglect of hhe above ratios M1 and M2 is a cause of waste in design effort of suspension insulators and that such neglect hampers both the designing of efficient and proper dimensions of the suspension insulators and the size reduction of the suspension insulators.